Error analysis in assessing respirator protection factors.
Appl Occup Environ Hyg 1995 Jul; 10(7):606-615
Examples were presented of the calculation of absolute and relative variance in the assessment of air contaminant concentration. The greatest effect on the standard deviation of the concentration was contributed by the variable whose value was closest to its accuracy of measurement. The workplace protection factor (WPF) of a mask was defined. A plot of aerosol concentration outside of a mask versus the coefficient of variation showed that the relative error was greater than acceptable limits for precision at WPFs greater than two. Bias errors in WPF measurements were demonstrated by the derivation of equations corresponding to a lack of compliance in use of a respirator. The fraction of noncompliance time (f) was defined as the time in which the mask was not worn divided by the total time. In this case, only an effective protection factor (EPF) could be calculated. Relating a calculated EPF to a hypothetical WPF if 100% compliance had been achieved was discussed. The ratio of the contaminant concentration when the mask was worn to the concentration when the mask was not worn was designated as a D- ratio. It was shown that the EPF and WPF were equivalent at higher f-values for lower WPFs and higher D-values. A table of acceptable f-values for a 25% bias error was provided. An equation for the analysis of small errors on bias estimates implied that for f-values less than 0.1, the relative errors in estimating f-and-D have equal effects on the relative precision of estimating WPF from EPF. The author concludes that the derived equations are useful in interpreting the effects of noncompliance on WPF.
NIOSH-Publication; NIOSH-Grant; Respirators; Analytical-processes; Respiratory-protection; Protective-equipment; Aerosols; Face-masks; Air-quality-measurement
William Popendof, Department of Preventive Medicine and Environmental Health, The University of Iowa, Iowa City, Iowa 52242-5000
Applied Occupational and Environmental Hygiene
University of Iowa, Iowa City, Iowa